It has previously been proposed to use Radio Frequency Identification (RFID) transponders with CDs or DVDs, and U.S. Patent Publication No. US2002/0175818A1 discloses such a device in FIGS. 18 and 19. However, the disclosed device includes a central conductive area spaced apart from the normal conductive area by a narrow peripheral slot, so that the primary antenna configuration is that of a fairly small slot antenna, with severely limited range. The configuration also employs conducting tabs which extend to the periphery of the disc, but the predominant radiation is from the relatively small area slot antenna.